1. Field of the Invention
The present invention generally relates to monolithic microwave switch matrices and, in particular, to such matrices which may be cascaded to form a larger matrix.
2. Statement of the Prior Art
Switch matrices are commonly used in complex communication equipment wherever great flexibility is required in the coupling of any number of signals to any number of terminals. The most desirable switch matrix is typically a full access matrix in which any one or more of a multiplicity of input terminals of the matrix can be simultaneously connected to any one or more, or different combinations of, a multiplicity of output terminals thereof. When the frequencies of the signals handled by such matrices reach into the gigahertz range and above, many problems are encountered in the distribution of the received input power. One approach at solving these various problems is described in U.S. Pat. No. 4,731,594 for a "Planar Active Component Microwave Switch Matrix and Airbridge for Use Therewith" and its related U.S. Pat. Nos. 4,611,814 and 4,609,889 for a "Microwave Frequency Power Divider" and a "Microwave Frequency Power Combiner", respectively. This approach uses field effect transistors, FETS, as amplifiers for dividing power from the input lines and also for combining power into the output lines to enable full access switching and to prevent power loss which would prohibit the construction of large switch matrices.
Similar power distribution problems have also been addressed in the area of distributed amplifiers as evidenced in the article "High Yield, 0.4 W, 2-18 GHz GaAs Distributed Amplifiers" by W. Cooper, et al., Coolied Microwave, May 1989, pages 98-106. The article describes distributed amplifiers comprised of a multiplicity of FETs which receive input signals parallel from a transmission line. The effect of the gatesource capacitance of the FETs on the transmission line is countered by inductance built into the line creating a lumped equivalent transmission line.
Important considerations in the construction of switch matrices are full access switching, the designing of cascadeable modules to allow easy tailoring of a matrix to a variety of systems without extra expense, the power distribution of very high frequency signals over a potentially large number of matrix switch points, the construction of crossovers between input and output transmission lines providing isolation therebetween and consistent transmission characteristics among crossovers, and the usual size, cost and power requirements.